This invention relates to a method for extruding solid or tubular products using a hot lubricant, including means for removing the deposit of carbonized lubricant on the surface of each extruded product in a reliable and easy manner simultaneously with the extruding phase of operation thereby improving the quality of the extruded products and facilitate the aftertreatments thereof.
There are known in the art various methods for producing solid or tubular bodies by metal extrusion, including the non-lubricated extrusion which is widely used for non-ferrous materials (e.g., aluminum and copper alloys). Also known are the extrusion with a glass lubricant and the extrusion with a carbon-base lubricant which are used mainly for steel materials, or the hydrostatic extrusion which is applicable to a wide variety of metallic materials. It is also known that the extrudability of a non-ferrous metal material can be improved to a significant degree by the use of the carbon-base lubricant extrusion or the hydrostatic extrusion method. For example, with a given press power, it becomes possible to work a billet at a higher reduction rate or to work a billet of a lower temperature. In the case of an aluminum alloy material, it is possible to enhance the productivity by speeding up the extrusion without incurring defects. However, these extrusion methods invariably have a problem in that the quality of the products is greatly impaired by the carbonized lubricant which deposits on the surfaces of the extruded products. For instance, the lubricated extruding means in which a billet precoated with a carbon-base lubricant is loaded into a container after heating and extruded through a die and/or a mandrel or in which the container as well as the die and/or mandrel is anointed with a carbon-base lubricant prior to loading a heated billet in the container for extrusion and the hydrostatic extrusion means in which a hot billet loaded in a container is extruded by the pressure medium applied to the ambient of the billet (with the forced lubricating effect of the pressure medium) have a common problem in that the surfaces of the extruded tubular product are darkened due to the deposition of a carbide of the used lubricant, which is formed by the extrusion at a high temperature. The carbide deposit on the extruded product not only lowers its value but also causes a corrosion when the tubular product is used as a condensor tube of a heat exchanger or the like. The deposit of carbonized lubricant gives rise to a similar problem even when an iron-base material is extruded with the use of a carbon-base lubricant. Although the carbide deposit on the outer surfaces of the solid or tubular extrudate are removed in a case where the extruded tube or rod is drawn through a drawing die in a subsequent stage, it is difficult to wash off the carbide deposit from the inner surfaces of the tube by pickling or the like. In addition, as the diameter of the tube or rod is reduced in the drawing stage, the pickling operation, which is troublesome in itself and requires complicated operations for the disposal of the spent liquor, should be avoided if possible from the standpoint of productivity and economy. Especially where a narrow tube of about 10-30 mm in diameter and in excess of 700 mm in length is extruded, it is practically difficult to remove the deposits on the inner surface of the extruded tube completely by a pickling a similar treatment. Therefore, a need still exists for long and thin tubes having clean inner surfaces after extrusion. In the absence of appropriate technology, there is a strong demand for a technical solution to this problem.